The present invention relates to a laser surveying system and a distance measuring method for projecting a laser beam to an object to be measured and for measuring a distance by receiving a light reflected from the object to be measured.
As an electro-optical distance measuring system, a laser surveying system is known, which projects a laser beam as a distance measuring light to an object to be measured and measures a distance to the object to be measured by using a light reflected from the object to be measured.
When a laser beam is projected to an object to be measured and electro-optical distance measurement is performed, a point on the object to be measured where the laser beam is projected is not necessarily on a flat surface, and the point may be an edge where flat surfaces cross each other. Because the laser beam has a certain spreading, a luminous flux of the beam has an area, and the condition on the projected surface of the object to be measured exerts influence on the results of measurement.
For this reason, for the purpose of improving the distance measurement accuracy in the electro-optical distance measurement, it is desirable that a beam diameter (spot size) of the laser beam is as small as possible.
As the laser beam used for a distance measurement light, it is preferable that near-infrared light with a wavelength of 1.4 μm to 2.6 μm is used. The near-infrared light is an invisible light. Even when the laser beam is projected into a human eye, no uncomfortableness is caused and the near-infrared light hardly injures the eye. On the other hand, the near-infrared light has a long wavelength and is easily influenced by interference. As a result, the spreading angle is increased. The spot size of the laser beam projected to the object to be measured is increased, and this leads to the decrease in the measurement accuracy.
In the past, the beam diameter is set to match the measuring ability of the laser surveying system, and to have an adequate value to match a standard distance to be measured, e.g. an average distance to be measured, and average measurement accuracy is improved.
In this respect, in the conventional type laser surveying system, there has been a tendency that error is increased when the actual distance to be measured is deviated from the standard measurement distance. In particular, in case near-infrared light is used as the distance measuring light, the spreading angle is big, and there has been a tendency that bigger error is caused when the distance to be measured is deviated from the standard measurement distance.